Effects of bottom and top layers of Niutitang Formation on preservation of shale gas in southern Guizhou

Lithology of the bottom and top layers of the Lower Cambrian Niutitang Formation plays an important role in evaluating the preservation conditions of shale gas in southern Guizhou. Based on outcrops and drilling data of the bottom layers of the Niutitang Formation, the studied area can be divided into the dolomitic rock zones, the mixed siliceous-dolomitic rock zones and the siliceous rock zones. Due to its ultra-low porosity, ultra-low permeability and high breakthrough pressure, siliceous rock is the best bottom layers for the preservation of shale gas. According to outcrops and drilling data of the top layers of the Niutitang Formation, the studied area can be divided into mudstone zones and limestone zones. The mudstone zones with low porosity, low permeability and high breakthrough pressure, so they are better than the limestone zones in the preservation of shale gas. Eastern Cengong-Sandu region is the most favorable area for exploring shale gas because of its siliceous rock bottom layers and mudstone top layers.